tl;dr I think one of my players is appropriating a character I've had since 2012, is this ok and if not can I get some help?
I'm running a new system that quote-unquote "came out" in November (tl;dr we got a starter kit, no character creation rules - everything's homebrew). It's a superhero themed RPG - you know, comic books, nemesis stuff, etc. So if some of this doesn't make much sense, that's the context.
One of my players has been really kind of forceful about one of the NPCs. The NPC in question is a werewolf berserker character, to give a short-hand: she fights people because she enjoys it, and she's kind of rash but knows how to control herself despite her rules. I've been working on her since... 2012? She's a problem but not in the same sense that several of my other NPC plans are - she wouldn't aim to kill the players and she's almost friendly despite the fact she's being paid to be an antagonist.
I ran a test to see if I could even really GM (I still don't feel like I'm doing a good job lol), and since then this one player got very 'attached' to the werewolf NPC. He kind of thrusts on her his own agenda/characterization and tries to twist her into a being that's falling to her instinct for the sake of being a foil to his own PC who combats her instincts. He also uses said twisted characterization to imply the two should fight frequently and often when asked to explain he uses an old, phased out character trait of Werewolf Girl that I brought up in passing once to justify himself, as well as a currently non-canon scene to our campaign that was from the test campaign. It came to a head yesterday and thus why I'm nervously posting here - he, out loud, wondered what it would take to break her despite the fact he acknowledged she wasn't his character.
He is, by the by, playing a hero character in a Superhero RPG.
At worst during sessions, this guy is your standard inactive player who doesn't do much unless prompted and honestly comes off like he doesn't pay any attention. I don't want to player kill, but I also feel steadily uncomfortable with the fact he downright implied he wanted to maim an antagonist for what comes off as "just because", coupled with his constantly confused behavior as if he doesn't quite understand what's going on. I believe he's new to pen and paper RPGs, so I want to know what I should do about him. Any advice?